1. Field of the Invention
The present invention relates a filter, particularly a filter with a through-hole.
2. Description of the Related Art
Various techniques about the air cleaning in the living space are traditionally developed from long ago. The filter formed of the thin film with a through-hole is mainly used to filter the components in a solution, and the filter that comprises the through-hole structure formed by an aluminum anodic oxide coating is on the market. On the other hand, except for the filtering by making use of the difference of the through-hole size, there is a reference described about the filter, which comprises a through-hole and selectively filters the gas molecules by making use of the difference of the gas diffusion rate in the through-hole. A non-patent literature 1 reports that it is possible to filter the gases which have various molecular weights by using the thin film which is made of aluminum anodic oxide and whose bore is about 20 nm. This filter makes use of the fact that the gas diffusion velocity in the through-hole is in proportion to the molecular weight of the gas to the −½th power, in case that the bore of the through-hole is corresponding to the mean free path of the gas (the bore of the through-hole is about 70 nm in the case of atmospheric gas).
The title of non-patent literature 1 is “Journal of Chemical Engineering of Japan 17,514 (1984)”.
It is effective to use flexible resin material in order to mass-produce the filter making use of the filtering by the difference of the size and the difference of gas diffusion velocity. On the other hand, in the filter with a fine through-hole, it is necessary to thin the thickness of a through-hole film portion to about from 0.5 to 2 μm, in terms of the increase of the gas permeability rate after filtering. Therefore, it is necessary to contrive in order not to damage the filter, when the mechanical strength of the filter is weak and a plurality of filters is used by being stacked one on another, or the filter is wound by a reel at the time of manufacture. There is a way to form a structure reinforce portion whose thickness is large side by side with the through-hole film portion in the filter as a typical way to give the mechanical strength to the filter with the fine through-hole. But, for example, there is a problem that the upper surface of structure reinforce portion damages the filter which is adjacent to the structure reinforce portion when the filter is wound by the reel, and the yield rate of the filter with fine through-hole declines.
The object of the present invention is to offer the resin filter with fine through-hole whose damage is reduced.